3 Replies Latest reply on Feb 6, 2013 10:56 AM by Dan_O

    RAID 0 And Defragmentation - Who Knows The Answer ?

    Stubi

      I have been a long time RAID 0 user. But I never found a real answer to the question if it is useful to defragment a RAID 0 area. Since Windows sees only 1 drive it will just move around the files according to the information in the windows file directory - so in the end it will just defragment the file index. But is this improving anything on the RAID 0 area?

       

      I guess the controller will just move the file data to areas where it finds space. It will not care about the windows defragmentation idea. Is this correct?  If so defragmentation would be just a waste of time - even worse - could move sequential information on the disks to a new location where they might not be sequential anymore. There is no control over it and there is no tool for real RAID 0 defragmentation. Is this correct?

       

      Who knows the answers (please no guessing - the internet is full of it)?

        • 1. Re: RAID 0 And Defragmentation - Who Knows The Answer ?
          Stubi

          Somehow I had the hope someone from Intel could clarify this mystery since in the end (only) they know how their RAID driver works. Sadly it did not happen. So the mystery will never be solved and the endless guessing on the internet will continue.

          • 2. Re: RAID 0 And Defragmentation - Who Knows The Answer ?
            john_s@intel

            RAID arrays appear to the operating system as a single disk drive. So you can use any defrag program that you would normally use with a disk drive.

             

            Operating systems utilities look at the drive through the operating system. The operating system detects and accesses the entire array of drives, as a single drive. The operating system doesn't even know you have multiple drives configured together as a single logical unit. The RAID process, is done at the hardware (controller) level and is a function of the controller and doesn't effect the OS or the applications installed.

             

            However, to be safe, I'd strongly recommended that you perform regular, verified data backups.

             

            Regards,

            John

            • 3. Re: RAID 0 And Defragmentation - Who Knows The Answer ?
              Stubi

              First off all John thank you very much for your response.

               

              I know that the OS does not care that RAID 0 is running and sees every RAID 0 area as a single disk. But the question then is does it make ANY sense to defragment a RAID 0 area. Windows cannot move/control the data on the hard disk but only on the logical system level. So in the end the defragmentation will just keep the RAID - controller and the hard disk busy but not position any data in a better not defragmented way on the hard disk itself. This would mean that there cannot be achieved any noticeable performance gain by the Windows defragmentation tool. So don't torture your RAID 0 system with it.

               

              One might think now RAID 0 is a bad idea in the end because fragmentation cannot be avoided. But then you have to see what you lose at access time and what you win at transfer time. But anyhow - only SSD RAID 0 would bring the perfect fix in the end. SSD RAID 0 with TRIM is now available starting with the 77 boards at least to my knowledge. My next board will have it for sure. At SSDs defragmentation is no topic anymore. There are no access arms that have to be moved. Just pointers to memory cells and this is a calculation.

               

              In respect of backups. If you have a single disk or a RAID 0 setup - you always need backups. And I have to say my Intel RAID 0 with 3 x 1 TB disks is very stable. I never had so little problems with any single disk configuration and I changed the cable order, switched off the power while it was working, changed the driver and whatever... Could not kill it or achieve any bad data. Of course I do not use the write cache.

               

              Regards,

               

              John (here too)

              • 4. Re: RAID 0 And Defragmentation - Who Knows The Answer ?
                Dan_O

                That is sort of correct.  Although Windows doesn't have access any lower than the virtual drive, there is still a 1:1 correlation between the addressing on the virtual drive, and the locations on the physical drives.

                 

                Defragging a RAID 0 will have an affect on the physical location of data on the drives.

                • 5. Re: RAID 0 And Defragmentation - Who Knows The Answer ?
                  Stubi

                  @Dan_O

                   

                  You write that there is still a 1:1 correlation between the addressing on the virtual drive and the locations on the physical drives.

                   

                  Lets take a 4 disk RAID 0 area and the data on it:

                   

                  A1 A2 A3 A4

                  A5 B1 C1 C2

                  C3 D1 D2

                   

                  A, B.. are different data records in this case still in a somehow orderly way. So how would Windows know about this order on the physical disk? In the end it could even look like this on the real disks:

                   

                  A2 B1 A2 A3

                  C1 A4 D1 C2

                  D2 C3 A5

                   

                  How can Windows now defragment this? From my point of view it can sort the LOGICAL index in Windows like this

                   

                  A1 A2 A3 A4 A5 B1 C1 C2 C3 D1 D2

                   

                  But it has no information about the real data location on the disk - it does not get this information and it cannot even guess it. RAID 0 does not store the data like this on the four disks:

                   

                  A1 A2 A3 A4

                  A5

                  B1

                  C1 C2

                  D1 D2

                   

                  If so it would waste a lot of space.

                  • 6. Re: RAID 0 And Defragmentation - Who Knows The Answer ?
                    Dan_O

                    Your third image is incorrect.  To Windows, it would look like:

                    A2 B1 A2 A3  C1 A4 D1 C2 D2 C3 A5